The present invention relates to a vehicle drive motor control system, and specifically, relates to a vehicle drive motor control system that, when a vehicle drive motor is in a locked state, urges a driver to make a switch from actuation of an accelerator to actuation of a brake, thereby preventing thermal damage to coils inside the motor.
In vehicles, such as electric vehicles and series hybrid vehicles, that are moved by a vehicle drive motor, in general, a three-phase alternating-current motor is used, and for example, when such a vehicle is held stopped on an uphill road by actuating an accelerator, rather than using a brake, current is continuously applied to only one phase of the coils inside the motor, which may cause overheating or failure of the coil to which current is applied.
In a conventional vehicle drive motor control system, as illustrated in FIG. 5, when a driver holds the vehicle stopped on an uphill road by actuating an accelerator, a vehicle drive motor enters a locked state, and if the temperature of a coil inside the motor exceeds a set value A, the current applied to the coil is limited to decrease the drive torque, thereby avoiding overheating or failure of the coil. However, when the temperature of the coil exceeds the set value A, if the current applied to the coil is suddenly limited for suppression of increase of the coil temperature, in a current-limitation period B, the accelerator is disabled because of the decrease in drive torque of the motor, resulting in deterioration in drivability.
Therefore, among the conventional vehicle drive motor control systems, there is one in which if it has been determined that a vehicle drive motor is in a locked state, a torque decrease limitation for decreasing a drive torque of the vehicle drive motor at a predetermined decrease ratio and then increasing the decreased drive torque at a predetermined increase ratio is provided, and at least one of the predetermined decrease ratio and the predetermined increase ratio is adjusted so that an average torque during the torque decrease limitation is a torque threshold based on which the temperature of a coil of a particular phase can be used as a base for temperature compensation of coils of the other phases (JP 2010-11545 A).
Also, among the vehicle drive motor control systems, there is one in which when it has been determined that a vehicle drive motor is in a locked state, a first torque decrease limitation for temporarily decreasing a drive torque of the vehicle drive motor and then returning the decreased drive torque to the original drive torque before the decrease is provided, and if the locked state is still not cancelled, a second torque decrease limitation for decreasing the drive torque of the motor to a predetermined torque, which is lower than the torque attained as a result of the decrease in the first torque decrease limitation, is provided (JP 2010-11546 A).
However, with a vehicle drive motor control system in which a drive torque is limited according to the degree of overheating of a coil inside a motor, as illustrated in FIG. 5, once the temperature of the coil increases beyond a set value A, the limitation of the drive torque cannot be cancelled until the coil temperature decreases to a temperature equal to or below the set value A, and thus, a state in which the drive torque cannot return to the original drive torque before the limitation lasts for a long period of time.